Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

If the earth stopped

  1. Jan 29, 2014 #1
    So I was just thinking about what would happen if the earth stopped rotating on it's axis. Everything unattached would be thrown into the air. The questions been bugging me for a while, how would you calculate the air resistance on objects thrown into the air? All I have to go on is that the earth rotates at about 1,670 kph.
     
  2. jcsd
  3. Jan 29, 2014 #2

    Drakkith

    User Avatar

    Staff: Mentor

    You wouldn't be thrown into the air, but would be violently thrown sideways as the Earth suddenly stopped rotating underneath you. The closer you are to the equator, the worse it is.
     
  4. Jan 29, 2014 #3
    So the air resistance wouldn't really factor in, anything on the earth would just be pushed onto the ground, basically?
     
  5. Jan 29, 2014 #4

    FactChecker

    User Avatar
    Science Advisor
    Gold Member

    Don't forget that the air would also want to keep moving, creating a wind from West to East. The resulting wind would would be slowed as the air near the ground gets dragged to a stop.
     
  6. Jan 29, 2014 #5
    So immediately after being pushed into the ground, there would be giant gusts of wind. Because the air will take longer to adjust to the stationary earth than a physical object.
     
  7. Jan 29, 2014 #6
    Nobody said anything about being pushed INTO the ground. As I recall Drakkith said violently sideways.
    The thing is how are you managing to distinguish what is part of the earth, and what is not? Is it everything but you?

    If the air is not part of your earth, and the air continues its motion, what do you think will happen to the birds and planes that fly in the air, and all else that moves with the air?
     
  8. Jan 29, 2014 #7
    I guess I hadn't thought too much on what exactly is the earth. Just thinking about stuff. But I guess I would say that the air is not part of the earth. The earth would be the ground, like dirt, mud, rocks, etc. But other things like buildings wouldn't be earth.

    That's an interesting idea, the relation between the birds/planes and the atmosphere. Let's change the definition of earth just for a second to include planes/birds. Would there then be a harsh wind that could potentially crash planes? That would be my guess anyways. And if the earth did not include the atmosphere, then the air would gradually slow because of friction. I wonder how much of an effect that would have on a plane?
     
  9. Jan 30, 2014 #8
    The plane would be attempting to fly with a wind in the neighborhood of 1670kph at the equation. Not too many planes are built to fly that fast. Mach 1 is about 1235kph.

    If the planes and air together did not stop like the rest of the earth, it should be able to continue flying. The air slowing would become a headwind or tailwind, but as long as the plane could keep its wind-speed within its operating performance then it should be able to continue along. Landing would be a problem until the air slowed down to less than 50kph as a round figure - whatever is normal presently before they close an airport due to high winds. If there is a serviceable airport left anymore after all the chaos.
     
  10. Jan 30, 2014 #9

    Nugatory

    User Avatar

    Staff: Mentor

    What is the water in the oceans doing? Either it counts as "earth", or we're getting some exciting flooding and very different outcomes at the two poles (one is ocean, one is on land).
     
  11. Jan 30, 2014 #10

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    @yoyopizza
    You never said how long it would take to bring about this state of affairs. Would it be achieved by some fancy 'gravity machine' that would slow everything down at once or would it apply a 'brake' to the Earth's mantle?
    Life could be very difficult during the transition - like when the bus driver slams on the brakes and everyone has shopping, kids in buggies or is just very old and infirm.

    What about the sea - sloshing around for several days and probably washing everyone off all the land below about 500m - a serious Tsunami situation.

    Once it had all settled down, there would be a rush for available living space at a suitable latitude where you could cope with 365X24 hour days. You would need 'shade loving desert plants' which could handle extreme cold to supply the food.

    But I think there are a few basics about gravity and circular motion that you need to sort out. The effect of the Earth's spin is so little that it is only just possible to measure the difference in the weight of an object at the Equator or at the N Pole. The Earth would need to be rotating at around 1 rev per 90 minutes for things to have zero effective weight at the Equator. 1 rev per 24 hours is hardly worth bothering about.
     
  12. Jan 30, 2014 #11
    Need to know what is supposed to happen to all of the Earth's angular momentum... are we assuming it just disappears? Because there is a ridiculously huge amount of energy there, which would have to end up somewhere.
     
  13. Jan 30, 2014 #12

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The earth will eventually stop rotating (if it lasts long enough) due to dissipation of energy from to tidal forces (due to gravitational forces of the moon on the oceans and earth crust). It is about 28 seconds each century (ie. the length of the day increases by about .8 milliseconds from one century to the next). The angular momentum of the earth - moon system however, cannot change so this loss of angular momentum of the earth results in an increase of the angular momentum of the earth-moon orbital system, so the distance between the earth and the moon increases.

    AM
     
  14. Jan 30, 2014 #13

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Not "stop", I think but it will slow up till it faces the Moon in its orbit - just as the Moon faces us. The Moon is moving away and the momentum is being redistributed.
     
  15. Jan 30, 2014 #14

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Right. It will become tidally locked so that the same side of the earth will keep facing the moon. The rotation period relative to the sun (i.e. our day) will be the length of the lunar month at the time tidal locking occurs.

    AM
     
  16. Jan 30, 2014 #15

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Given sufficient time and no other planets in the solar system, the Earth's orbit could also increase in radius and it could become locked to the Sun.
    But the total Angular Momentum in the Solar System mostly lies with the orbits of the major planets so the whole thing would need some serious readjustment for the Earth to behave, in its orbit like the Moon behaves around Earth.
     
  17. Feb 3, 2014 #16
    Am wondering to what extent the Earth’s magnetic field would be affected. Would a cessation of the earth’s rotation (including the mantle and core) mean there would be no magnetic field, or is some of the field generated by convection? If the core and mantle stopped rotating, how long would they remain magnetic enough to protect against the solar wind and other radiation?

    .
     
    Last edited: Feb 3, 2014
  18. Feb 3, 2014 #17

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Rather than discussing a very loosely defined 'horror / disaster' transition scenario, it might be more fruitful to discuss what conditions would be like on a similar planet to Earth, in similar conditions, where there happens to be no (or very slow) rotation and where that situation has obtained for many millions of years.
    You could then discuss how things might have evolved without a magnetic field, without tides (or surface water?) with temperatures that vary over one year, rather than over a day.
    The OP is more Hollywood than Physics, I think.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: If the earth stopped
  1. If earth stops rotating (Replies: 19)

Loading...